Constructing hyperbolic systems in the Ashtekar formulation of general relativity

Hyperbolic formulations of the equations of motion are essential technique for proving the well-posedness of the Cauchy problem of a system, and are also helpful for implementing stable long time evolution in numerical applications. We, here, present three kinds of hyperbolic systems in the Ashtekar formulation of general relativity for Lorentzian vacuum spacetime. We exhibit several (I) weakly hyperbolic, (II) diagonalizable hyperbolic, and (III) symmetric hyperbolic systems, with each their eigenvalues. We demonstrate that Ashtekar's original equations form a weakly hyperbolic system. We discuss how gauge conditions and reality conditions are constrained during each step toward constructing a symmetric hyperbolic system.Comment: 15 pages, RevTeX, minor changes in Introduction. published as Int. J. Mod. Phys. D 9 (2000) 1

Probabilistic analysis of the upwind scheme for transport

We provide a probabilistic analysis of the upwind scheme for multi-dimensional transport equations. We associate a Markov chain with the numerical scheme and then obtain a backward representation formula of Kolmogorov type for the numerical solution. We then understand that the error induced by the scheme is governed by the fluctuations of the Markov chain around the characteristics of the flow. We show, in various situations, that the fluctuations are of diffusive type. As a by-product, we prove that the scheme is of order 1/2 for an initial datum in BV and of order 1/2-a, for all a>0, for a Lipschitz continuous initial datum. Our analysis provides a new interpretation of the numerical diffusion phenomenon

Hydroxyethyl cellulose matrix applied to serial crystallography

Serial femtosecond crystallography (SFX) allows structures of proteins to be determined at room temperature with minimal radiation damage. A highly viscous matrix acts as a crystal carrier for serial sample loading at a low flow rate that enables the determination of the structure, while requiring consumption of less than 1 mg of the sample. However, a reliable and versatile carrier matrix for a wide variety of protein samples is still elusive. Here we introduce a hydroxyethyl cellulose-matrix carrier, to determine the structure of three proteins. The de novo structure determination of proteinase K from single-wavelength anomalous diffraction (SAD) by utilizing the anomalous signal of the praseodymium atom was demonstrated using 3,000 diffraction images. ? 2017 The Author(s).113Ysciescopu

Atomic layer deposition of PbCl2, PbBr2 and mixed lead halide (Cl, Br, I) PbXnY2-n thin films

Atomic layer deposition offers outstanding film uniformity and conformality on substrates with high aspect ratio features. These qualities are essential for mixed-halide perovskite films applied in tandem solar cells, transistors and light-emitting diodes. The optical and electronic properties of mixed-halide perovskites can be adjusted by adjusting the ratios of different halides. So far ALD is only capable of depositing iodine-based halide perovskites whereas other halide processes are lacking. We describe six new low temperature (Peer reviewe

Freedom of choice to migrate: adaptation to climate change in Bangladesh

Adaptation is an essential part of climate change policy. In areas where impacts are likely to be severe, migration is considered to be an adaptation option. In Bangladesh coastal areas migration due to climate change is contingent on people’s freedom of choice at individual and household level. Following Amartya Sen’s capability approach, we argue that there should be a line drawn between migrations by free choice versus forced migration. Sen’s capability approach focuses on the importance of people’s freedom of choice to act, and the ability to achieve what they consider valuable in their life. In this paper, we use an extensive empirical work engaging 22 focus groups discussions (8–12 individuals in each group) and 14 Key Informants Interviews in South-West Bangladesh to elicit how freedom of choice changes with the economic class and social status of an individual. Using these data we apply Sen’s capability approach to understand the role of the freedom of choice when considering migration as an adaptation option. We argue that the capability approach is essential in revealing a thin border between migration as a (planned) adaptation option and forced migration

Comparative study of deuterium retention and vacancy content of self-ion irradiated tungsten

Self-ion irradiation of pure tungsten with 2 MeV W ions provides a way of simulating microstructures generated by neutron irradiation in tungsten components of a fusion reactor. Transmission electron microscopy (TEM) has been used to characterize defects formed in tungsten samples by ion irradiation. It was found that tungsten irradiated to 0.85 dpa at relatively low temperatures develops a characteristic microstructure dominated by dislocation loops and black dots. The density and size distribution of these defects were estimated. Some of the samples exposed to self-ion irradiation were then implanted with deuterium. Thermal Desorption Spectrometry (TDS) analysis was performed to estimate the deuterium inventory as a function of irradiation damage and deuterium release as a function of temperature. Increase of inventory with increasing irradiation dose followed by slight decrease above 0.1 dpa was found. Application of Positron Annihilation Spectroscopy (PAS) to self-irradiated but not deuterium implanted samples enabled an assessment of the density of irradiation defects as a function of exposure to highenergy ions. The PAS results show that the density of defects saturates at doses in the interval from 0.085 to 0.425 displacements per atom (dpa). These results are discussed in the context of recent theoretical simulations exhibiting the saturation of defect microstructure in the high irradiation exposure limit. The saturation of damage found in PAS agrees with the simulation data described in the paper. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )Peer reviewe

Native sulfur/chlorine SAD phasing for serial femtosecond crystallography

Serial femtosecond crystallography (SFX) allows structures to be determined with minimal radiation damage. However, phasing native crystals in SFX is not very common. Here, the structure determination of native lysozyme from single-wavelength anomalous diffraction (SAD) by utilizing the anomalous signal of sulfur and chlorine at a wavelength of 1.77 angstrom is successfully demonstrated. This sulfur SAD method can be applied to a wide range of proteins, which will improve the determination of native crystal structures.open112633sciescopu

Redox-coupled proton transfer mechanism in nitrite reductase revealed by femtosecond crystallography

Proton-coupled electron transfer (PCET), a ubiquitous phenomenon in biological systems, plays an essential role in copper nitrite reductase (CuNiR), the key metalloenzyme in microbial denitrification of the global nitrogen cycle. Analyses of the nitrite reduction mechanism in CuNiR with conventional synchrotron radiation crystallography (SRX) have been faced with difficulties, because X-ray photoreduction changes the native structures of metal centers and the enzyme-substrate complex. Using serial femtosecond crystallography (SFX), we determined the intact structures of CuNiR in the resting state and the nitrite complex (NC) state at 2.03- and 1.60-angstrom resolution, respectively. Furthermore, the SRX NC structure representing a transient state in the catalytic cycle was determined at 1.30-angstrom resolution. Comparison between SRX and SFX structures revealed that photoreduction changes the coordination manner of the substrate and that catalytically important His255 can switch hydrogen bond partners between the backbone carbonyl oxygen of nearby Glu279 and the side-chain hydroxyl group of Thr280. These findings, which SRX has failed to uncover, propose a redox-coupled proton switch for PCET. This concept can explain how proton transfer to the substrate is involved in intramolecular electron transfer and why substrate binding accelerates PCET. Our study demonstrates the potential of SFX as a powerful tool to study redox processes in metalloenzymes.open113532sciescopu